<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
</head>

<body>
	<script>
		var a = 10;
		var obj = {
			a: 20
		}

		function fn() {
			this = obj; // 修改this，运行后会报错
			console.log(this.a);
		}

		fn();
	</script>
</body>

</html>